Transient response vs. tuner response with implications for HDTV

Luminance transient responses for an NTSC 2T-edged bar signal and baseband video responses are shown for ten different tuner responses permissible within representative tuner limits. Transient responses are shown to vary from 8% smear to 18% overshoot, primarily due to amplitude and group delay variations from low to medium video frequencies. This indicates the need for improvement if EDTV and HDTV (extended- and high-definition TV) are to meet consumer expectations for image quality. Additional distortion can result from echoes on the transmission line between antenna and tuner, each of which may have a frequency-dependent VSWR (voltage standing wave ratio) exceeding 4.0. The echo on a lossless line would be 36% (-8.9-dB) if VSWRs were frequency independent, and 4.0 at both ends. For a residential installation with 55 ft of 300- Omega twin lead, the first echo would be delayed 140 ns (half cycle of NTSC subcarrier).<
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